1. Field of the Invention
The present invention relates to an ink feeder in a keyless printing press or other printing presses. A keyless printing press refers to a printing press in which ink keys in a doctor of an ink source roller are omitted.
2. Description of the Prior Art
One example of a printing unit and an ink feed system in a printing press in the prior art is illustrated in FIG. 3. This printing press includes an ink feed system in which ink i within an ink feed tank 10 is sent under pressure to an ink feed nozzle 13 through piping 11 by means of an ink pump 12 and is fed to an ink source roller 1 by the ink feed nozzle 13. The press further includes a printing unit in which the aforementioned ink i is transferred to a blanket drum 6 via the ink source roller 1, a transfer roller 2, a doctor roller 3, an ink application roller 4 and a plate drum 5 which are rotating in the directions indicated by arrows, whereby printing is effected on a sheet p. Also, there is provided a wetting water device in which wetting water w within a wetting water tank 15 is transferred to the plate drum 5 via a water source roller 16, a brush roller 17, a water reciprocating roller 18 and a water application roller 19. And, furthermore, there is provided an ink recovery system in which surplus ink is scraped by means of a blade 14 disposed against the doctor roller 3 so as to be circulated to an ink feed tank 10.
The above-mentioned blade 14 entirely scrapes surplus ink containing wetting water from the doctor roller 3 to circulate the ink to the ink feed tank 10 where it is recovered. Hence, the wetting water w fed from the wetting water device is partly fed to the sheet p jointly with ink, partly evaporates into the atmosphere, and is partly scraped by the blade 14 under an emulsified condition. The ink is returned to the ink feed tank 10.
In the above-described ink circulation system provided with an ink recovery system, however, since moisture is not contained originally in the ink, the moisture content in the ink rises gradually, and eventually the moisture content of the ink is stabilized due to the feeding of wetting water to the sheet and the evaporation of the wetting water. In the present state of the art, a phenomenon arises in which wetting water made to adhere to a pattern portion is separated therefrom by ink made to adhere to the pattern portion due to a shearing force between the rollers, wherein the wetting water forms drops which fall into the ink feed tank 10. These water drops are observed on the ink surface within the tank in the form of a water pool. And, even in the piping 11 for feeding ink to the ink feed nozzle 13 by means of the ink pump 12, reemulsification would not occur, but water would flow in the portion of the same nozzle 13 back toward the tank. Consequently, water is not fed to the ink source roller 1 but falls again into the ink feed pump 12, and due to repeated circulation of the water, the moisture content in the ink being fed varies gradually. In some cases, there is a possibility of a deterioration in the quality of the printed surface caused by variations in the transfer of the ink.
Furthermore, in the case of color printing in blue, red and/or yellow, since the influence of the moisture content of ink on the printing quality is large in distinction from the case of black and white printing, it is necessary to regulate the moisture content to a low value.